Steel treatment



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Patented Nov. 28, 1939 i UNITED STATES PATENT OFFICE 2,181,693 STEELTREATMENT Samuel Epstein, Bethlehem, and Hugo C. Larson, Johnstown, Pa.,assignors to Bethlehem Steel Company, a corporation of PennsylvaniaApplication September 8, 1937, Serial No.162,848 12 Claims. (01. 75-56)This invention relates to controlling the rim- T avoid a wi d or str n yfalling steel on ming action of steel so that the solidified ingot theone hand and a rising steel on the other, a

has a thick-skinned butt which will not crack certain amount ofdeoxidizer has to be used in and tear during rolling and hence givebillets the ladle of low carbon steel in order to leave with goodsurface. the right amount of active oxygen in the steel. 5

Rimming steel gives off large quantities of The correct amount ofdeoxidizer can be judged gases (Co, N2, H C0 mainl arbo mehexfrom thecomposition of the bath and slag in the ide, while it is poured into theingot mold and f a U u y appreciably less d er is during solidification.This gas evolution causes added to the ladle than is likely to Produce a1i) the ingot to have a spongy structure without e Steel in the meld- Ifa Steel which falls any central shrinkage cavity or pipe. To elimip y inthe ds u t t falling t nd n y hate pipe and undue sponginess and to geta can e v r ome by adding the p -p amount tough-skinned t t t same trequires of the deoxidizer aluminum in the succeeding close control ofthe rimming action. melds- Fairly f y, owever, the corre t If the steelas poured contains too much reihE ladle addition nnot be judged acactiveoxygen and thus tends to give off too euretely n the Steel rises in themold. mmuch carbon monoxide it acts wild in the ming Steel Containing utP t ea m o pouring t meld n up rephhy t bon or higher invariably tendsto rise in the mold the molten metal which contains large bubbles evenwithout the addition of y deoxidizer in 30 of t evolving a Then as thgas Suddenly the ladle. In these instances it is advantageous escapesthe height of the metal in the mold sinks. to add some substance to e dlme d wh ch sharply d th m requires further fllling has an effect exactlythe opposite of a deoxidizer Such an ingot may sink again beforesolidifyand hence causes the steel to hold steady or ing so that a pipeis formed (sheet or strip rolled fell Slightly in the l instead ofrisingfrom such steel may also have the defect called The Obvious e p onor the formation of 25 lamination) or it may rise. In the latter casethe Pencil-like b ow es a the butts i the enlong pencil-like blowholesclose to the surface trepment of gases which a v d dur ng s of the ingotand perpendicular to it are formed lidification- In h upper half of theingot t at the lower portion or butt. The butt of such c s can escape tothe outer air e readily an i ot gives poor surface i rolling because ofthe smaller ferrostatic head of molten 30 We have found by experiencethat, if the steel metal. At the lower half Of the ingot OI butt aspoured contains the proper amount of reacthe greater ferrostatic head Ofthe molten metal ti xygen t form, t proper amount of 0 above can preventescape unless the evolved gas t metal n t m more Steadi1y After hassufiicient pressure to overcome the ferrofilling the metal holds itslevel and the surface Static Pressure If as solidification takes place,35 quickly assumes an active boiling appearance, the gases evolved atthe IOWGI part Of the ingot Soon the characteristic crust or rim beginsto are entrapped, the ingot naturally S S n the form from the sidesinward, from which the term moldrimming steel is derived. The crust orsolidified Ev n ly it is not enough for ga to be iven top of the ingotis either at the same level as ff arly n t p u period- The eases must 40that to which the molten steel was poured, or be evolved preciselyduring the time when solidia inch or two lower, s h an ingot h no pipefication is proceeding so that the gases evolved and fewer of the longpencil-like blowholes apat the surfaces of the solidifying crystals inthe pear at the butt so that it gives a better surface change from theliquid to the solid state, can be in rolling. swept out and can exertenough pressure to es- 45 On the other hand, if the steel as poured conptains too little reactive oxygen, too little CO is We have found that asimple and effective way evolved. The metal fills the mold steadily andto produce such a gas evolution is to add a strong retains its level butthe boiling action may be oxidizing substance to the steel, of the classof somewhat more sluggish. Then the ingot slowly strong oxidizers likepotassium chlorate, sodium 50 begins to rise in the mold, the amount ofrise nitrate, potassium permanganate, and potassium varying from an inchor two to as much as eight dichromate. Presumably the oxygen in the orten inches. Such an ingot has a thin-skinned strong oxidizer immediatelyforms FeO on combutt with large pencil-like blowholes which cause me inContact w the m t Steel- This P60 poor surface in rolling. along withthe Eco already present remains in 55 solution in the molten steel; butFeO is rejected by the solidified steel during solidification. As soonas the molten steel is enriched by this rejected FeO the latter reactswith the carbon in the molten steel according to the equationFeO+C=CO+Fe. Thus more CO is evolved at the surface of the solidifyingcrystals and this helps increase the gas pressure to above what it wouldbe if the strong oxidizer were not added. The gases evolved can thusescape.

Of the strong oxidizers sodium nitrate is the cheapest. It was found,however, that on adding it to the molds of rimming steel during pouringa rather loud explosion would occasionally occur. The tendency toexplode was completely eliminated by mixing the sodium nitrate withfinely powdered F6203. Our practice has been to fuse the sodium nitrateand add the powdered F8203 stirring up the mixture and casting it intolb. cakes. These cakes are very strong and are conveniently handled onthe pouring platform. For example, the proportions may be 60 partssodium nitrate to 40 parts F6203 by weight. This has been satisfactorybut a lesser or greater proportion of F9203 may also be used. The sodiumnitrate may run from 35% to while the ferric oxide may run from 65% to10%. The cast cakes of the oxidizing agent, of definite and moderateweight, are of considerable practical advantage in enabling the operatorto add amount of the re-agent. It is obvious that the amount of-re-agentnecessary will vary with the difierent castings, and the same cakes ofdefinite weight enable the operator to add the requisite amount in anyparticular instance. Cakes of the mxiture can also be made withoutfusing but by mixing dry, adding a suitable binder and molding underpressure in a die.

For low carbon rimming steel about 2 to 16 oz. per ton of the 60:40NaNO3 Fe203 mix are required depending upon the degree of deoxidation ofthe steel. ladle or mold, preferably the latter. For higher carbonrimming steel the amount of the mix required may be two to three timesthat for lower carbon steels. In using proper amounts of the mix notenough nitrogen isabsorbed from the sodium nitrate to harm the steel inany way. The i is conferred by adding the mix greatest benefit to arising steel. However, our work indicates that even in the case of afalling steel the addition of the mix gives an ingot with a somewhatthicker and sounder skin at the butt.

Figs. 1a and 127 show photographs of cross-sections through the buttsabout 12 inches from the bottom of two 22". x 25" rimming steel ingotsfrom the same heat. In A of ingot #3 no addition was made to the mold;in B of ingot #8, 1%.; lbs. of sodium nitrate was added to the 4-ton'ingot. Note the large pencil-like blowholes near the surface in theuntreated ingot and the nuch smaller blowholes further removed from thesurface in the treated ingot.

Figs. 2a and 2b show the contours of the tops of the same ingots. Ingot#3 with no mold addi tion rose about 3 inches, where as ingot #8 with anaddition of 1 lbs. of sodium nitrate'fell about 3 inches.

Figs. 3a and 3b show photographs of cross sections similar to those ofFigs. 1a and 1b of 2 ingots from another heat. Ingot #2 untreated hasnumerous large pencil-like blowholes near the surface. Ingot #4 treatedwith 1 lb. of a 3:3:4

sodium nitrate-sodium dichromate-FezOav mix shows no pencil-likeblowholes near the surface.

the necessary This amount may be added in the TABLE I.-Summary ofsurface defects in billets cut from ,the butts of 60 ingots from 6 heatsDefective areas-sq. in. per sq. ft. Mold addition N f I t A1" to:

o. 0 ago ga ingots seams scabs cracks hide ls l' gz liing t t 20 1.881.8 .08 8.0

0 mm in re. e F8203 mix 40 1.3 1.3 .07 .47

Note that alligator hide which is the most serious defect was almostcompletely eliminated by the mix. The amount of seams and scabs was alsomaterially reduced.

We appreciate the fact that various substances have previously beenadded to rimming steel for the purpose of controlling the rimmingaction.

. Sodium carbonate and calcium fluoride have been used or proposed foruse. We have found, however, that the best results in this control canbe obtained by using suchsubstances as those mentioned above, namelystrongly oxidizing substances. For characterizing the type of materialwhich we have found to be most effective,.they are such substances asare decomposed or dissociated to liberate oxygen at the temperature ofmolten steel, at the time of casting.

While we have referred tothefuse of F6203 for preventing the explosiveaction sometimes accompanying the use of strongly oxidizing substances,we do not desire to limit ourselves to the use of the particularsubstance F6203. Frequently its use is unnecessary. Furthermore, otherdiluents or interspersing agents may be employed. We prefer to use sucha diluent or interspersing agent as an oxide which is not broken down atthe'temperature of the molten steel at the time of tapping or casting.Roll scale, for example, may be successfully used.

Having thus described our invention what we claim as new and desire tosecure by Letters Patent is;

1. Themethod of manufacturing rimmed steel comprising the step of addinga highly oxidizing agent of the group comprising potassium chlorate,sodium nitrate, potassium permanganate and potassium dichromate andtheir equivalents .to the molten metal after tapping.

2;. The method of manufacturing rimmed steel comprising the step ofadding sodium nitrate tion of steel to obtain an ingot with athickskinned butt, comprising the addition to the molten rimming steelafter tapping of a mixture of an oxidizing substance of the groupcomprising potassium chlorate, sodium nitrate, potassium permanganate,potassium dichromate and their equivalents and a diluent of weakeroxidizing action than said oxidizing substance.

6..The method of controlling the rimming action of steelv to obtainaningot with a thickskinned butt, comprising the addition to the moltenrimming steel after tapping of a mixture of sodium nitrate and a diluenthaving a weaker oxidizing action than sodium nitrate.

7. The method of controlling the rimming action of steel to obtain aningot with a thickskinned butt, comprising the addition to the moltenrimming-steel after tapping of an oxygen containing substance of thegroup comprising potassium chlorate, sodium nitrate, potassiumpermanganate and potassium dichromate and their equivalents.

8. The method of controlling the rimming action of'steel to obtain aningot with a thickskinned butt, comprising the addition to the moltenrimming steel after tapping of sodium nitrate.

9. The method of controlling the rimming action of steel to obtain aningot with a thickskinned butt, comprising the addition to the moltenrimming steel after tapping of a sodium nitrate-iron oxide mixture, theproportions of this mixture varying from about 10 per cent to 65 percent iron oxide.

10. The method of controlling the rimming a ction of steel to obtainaningot with a thickskinned butt, comprising the addition to the moltenrimming steel afte'r tapping of a sodium nitrate-Fe'zOa mixture, theproportions of this mixture varying from about 10 percent to 65 per centF6203.

11.The method of controlling the rimming action of steel to obtain aningot with a thickskinned butt, comprising the addition to the moltenrimming steel while pouring in the mold of from 2 oz. to 48 oz. per tonof a sodium nitrateiron oxide mixture. r v

12. The method of controllingthe rimming action of steel to obtain aningot with a thickskinned butt, comprising the addition to the moltenrimming steel in the ladle of from 2oz. to 48 oz. per ton of asodiumnitrate-iron oxide mixture.

SAMUEL EPSTEIN. HUGO C. LARSON.

